So far it has been practiced to coat the surface of an object with hydrophobic materials such as silicon type compound or resin, fluorine-containing resin, polyolefin resin etc. in order to make the surface of an object difficult to be wetted, namely, to give a water-repellant property to the surface of an object. When water adheres to the surface of an object, which has been thus treated to make the surface hydrophobic, water is rejected to form a spherical waterdrop. While big waterdrops fall by their own weight, small waterdrops stay adhered strongly to the surface of the object and often do not fall even the adhered surface is leant vertically. In such a case a dry surface without waterdrops can be obtained only the adhered waterdrops is removed forcibly by a mechanical way such as wiping out.
Therefore, various development studies of highly hydrophobic materials have been conducted to make an adhered waterdrop as closely as possible to a sphere by making the hydrophobicity of the surface of an object as high as possible and increase the contact angle with water and thus to roll down the waterdrops from the surface of an object. Furthermore, physical methods such as making the surface rough or forming thin hairs on the surface are being studied. However, the materials so far proposed to make the contact angle with water big have problems such as being inferior in mechanical properties such as hardness, strength etc. or very special substances whose production is difficult. Moreover, in case of physical methods such as making the surface rough or forming thin hairs, there is problems that their effect lessen when the surface of an object is rubbed once.
Therefore, a development of coating material, which gives a water-repellant property to the surface of an object and at the same time can easily remove the adhered waterdrops sliding down from the surface of the object, is strongly desired.
The present inventors have largely changed the direction from the conventional idea of making the contact angle of the adhered waterdrop as big as possible and making the waterdrop as spherical as possible so that it easily rolls down from the surface of an object, and have been intensively studying to develop a material capable of forming a water-slidable surface from which a waterdrop easily slides down by its own weight, although the contact angle of the adhered waterdrop is not so big.
As a result, they found that a film formed by crosslinking and curing the reaction product, obtained by previously reacting a hydroxyl group-containing fluoropolymer with a certain kind of epoxy-terminated siloxane polymer in the presence of a sulphonic acid compound, with a crosslinking agent meets the above mentioned purpose and completed the present invention.